Specify target platform value in postinstall script

[RobMoloneyPILZIE]

We can currently specify the arch value using process.env.npm_config_arch, would it be possible to extend that to include the platform attribute. This would be helpful for cross-platform builds.

async function getTarget() {
const arch = process.env.npm_config_arch || os.arch();
const platform = process.env.npm_config_platform || os.platform();

switch (platform) {
    case 'darwin':
        return arch === 'arm64' ? 'aarch64-apple-darwin' :
            'x86_64-apple-darwin';
    case 'win32':
        return arch === 'x64' ? 'x86_64-pc-windows-msvc' :
            arch === 'arm64' ? 'aarch64-pc-windows-msvc' :
            'i686-pc-windows-msvc';
    case 'linux':
        return arch === 'x64' ? 'x86_64-unknown-linux-musl' :
            arch === 'arm' ? 'arm-unknown-linux-gnueabihf' :
            arch === 'armv7l' ? 'arm-unknown-linux-gnueabihf' :
            arch === 'arm64' ? 'aarch64-unknown-linux-musl':
            arch === 'ppc64' ? 'powerpc64le-unknown-linux-gnu' :
            arch === 's390x' ? 's390x-unknown-linux-gnu' :
                'i686-unknown-linux-musl'
    default: throw new Error('Unknown platform: ' + platform);
}

}